An oil well cement expansion agent and a method for preparing the same

Abstract

This invention discloses an oil well cement expanding agent and its preparation method, relating to the field of expanding agent technology. The oil well cement expanding agent is prepared from the following raw materials in parts by weight: composite expanding aggregate: 90-100 parts; interface activator: 3-8 parts; organic slow-release coating agent: 1.5-4 parts. The composite expanding aggregate is prepared from the following raw materials in parts by weight: calcium carbide slag: 30-45 parts; steel slag powder: 25-35 parts; desulfurized gypsum: 15-25 parts; metakaolin: 10-20 parts. The oil well cement expanding agent prepared by this invention eliminates the volume shrinkage of the cement ring from the plastic stage to the late hardening stage. In the early stage, the organic coating delays the reaction of free CaO in the calcium carbide slag, causing its expansion to occur before and after the initial setting of the slurry, effectively compensating for chemical shrinkage and plastic shrinkage, and preventing the formation of initial micro-annular gaps. In the middle stage, the large-scale and continuous generation of ettringite (AFt) provides strong expanding force during the critical period of cement stone structure formation.

Description

Technical Field

[0001] This invention relates to the field of expansion agent technology, specifically to an oil well cement expansion agent and its preparation method. Background Technology

[0002] In the exploration and development of oil and gas fields, cementing operations are a crucial step in ensuring wellbore integrity and achieving effective inter-layer isolation. Cementing quality directly affects the lifespan, production safety, and recovery rate of oil and gas wells. The cement sheath formed by the solidification and hardening of the cement slurry in the wellbore serves primarily to support the casing and isolate the formation.

[0003] However, during the hydration and hardening process, oil well cement inevitably undergoes volume shrinkage, primarily including chemical shrinkage, autogenous shrinkage, and water loss shrinkage. This shrinkage leads to the formation of micro-annular gaps at the cement sheath and casing (first interface) and at the cement sheath and wellbore (second interface). The presence of these micro-annular gaps severely weakens the sealing ability of the cement sheath, providing a channel for formation fluids (especially natural gas) to flow through, i.e., triggering "annular air channeling." This is one of the main causes of cementing failure, wellbore integrity problems, and safety accidents.

[0004] To compensate for the volume shrinkage of cement, the industry commonly uses the technique of adding cement expanding agents; existing oil well cement expanding agents are mainly divided into the following categories:

[0005] 1. Etnacite-based expanding agents: These expanders generate volume expansion by producing ettringite crystals. Such expanding agents (e.g., aluminum powder, calcium sulfoaluminate, etc.) are effective at room temperature. However, in the high-temperature environment at the bottom of the well (usually >110℃), ettringite will decompose into monosulfide-type hydrated calcium sulfoaluminate, resulting in a significant decrease or even loss of expansion efficiency, and may also cause strength reduction due to later transformation.

[0006] 2. Calcium oxide-based expansion agent: It expands by hydrating calcium oxide to form calcium hydroxide. Its hydration reaction is rapid, and the expansion mainly occurs in the early stage when the cement paste is still plastic. Most of the expansion energy is consumed by the fluidity of the paste, so the effective compensation capacity is limited, and it may cause structural damage due to excessive local expansion.

[0007] 3. Magnesium oxide-based expansion agent: It utilizes the hydration expansion of magnesium oxide. Its hydration rate is greatly affected by the calcination temperature (activity), which is difficult to control. High-activity magnesium oxide is prone to early and rapid reaction, while low-activity magnesium oxide may not expand in time or in sufficient quantity. The effect of using it alone is unstable, and high magnesium content may pose a potential risk to the long-term durability of cement stone.

[0008] Furthermore, existing high-performance expansive agents mostly rely on chemical raw materials, resulting in high costs. At the same time, industrial production generates a large amount of industrial solid waste such as carbide slag, steel slag, and desulfurization gypsum every year, which occupy land and pollute the environment when stockpiled. Although these solid wastes contain abundant active or potentially active components such as calcium, silicon, aluminum, and sulfur, their composition fluctuates greatly, their activity is low, or they contain undesirable components, so their direct application in oil well cement is often ineffective. Therefore, this application proposes an oil well cement expansive agent that can make full use of industrial solid waste, is low in cost, and has a simple process. Summary of the Invention

[0009] This invention provides an oil well cement expanding agent and its preparation method, aiming to solve the problems of existing oil well cement expanding agents such as reduced expansion efficiency, limited effective compensation capacity, unstable effect and high cost under high temperature environment.

[0010] Firstly, to achieve the above objectives, the technical solution adopted by the present invention is: an oil well cement expanding agent, prepared from the following raw materials in parts by weight:

[0011] Composite expanded aggregate: 90-100 parts;

[0012] Interface activator: 3-8 parts;

[0013] Organic sustained-release coating agent: 1.5-4 parts;

[0014] The composite expanded aggregate is prepared from the following raw materials in parts by weight:

[0015] Carbide slag: 30-45 parts;

[0016] Steel slag powder: 25-35 parts;

[0017] Desulfurized gypsum: 15-25 parts;

[0018] Metakaolin: 10-20 parts.

[0019] Furthermore, the particle size of the calcium carbide slag and steel slag powder is 5-80 μm, and the calcium carbide slag and steel slag powder account for 60-70% of the total mass of the composite expanded aggregate.

[0020] Furthermore, the particle size of the desulfurized gypsum and metakaolin is 0.5-5μm, and the desulfurized gypsum and metakaolin account for 30-40% of the total mass of the composite expansive aggregate.

[0021] Furthermore, the interface activator is composed of sodium sulfate, sodium silicate, and triethanolamine;

[0022] The mass ratio of sodium sulfate, sodium silicate and triethanolamine is 5:4:1, and its fineness is ≤10μm.

[0023] Furthermore, the organic slow-release coating agent is a composite wax powder prepared by melt mixing stearic acid and low molecular weight polyethylene wax at a mass ratio of 1:0.3-0.6 and then spray cooling.

[0024] The organic slow-release coating agent has a melting point range of 60-75℃ and a particle size of 10-30μm.

[0025] Furthermore, the molecular weight of the low molecular weight polyethylene wax is 2000-3000.

[0026] Secondly, the technical solution adopted by this invention is: a method for preparing an oil well cement expansion agent, comprising the following steps:

[0027] S1. Raw material pretreatment and activation:

[0028] S1.1 Dry the carbide slag at 105-120℃ until the moisture content is <1%, and then use an air classifier to separate the 5-80μm micron-sized carbide slag for later use.

[0029] S1.2. Add steel slag powder and metakaolin to a vertical stirred mill and mix thoroughly to obtain a mixture. Then add grinding aid at 0.5-1.0% of the weight of the mixture and grind together for 45-90 minutes to achieve a specific surface area of ​​550-750 m². 2 / kg, to obtain composite active powder;

[0030] S1.3 Calcine the desulfurized gypsum at 150-180℃ for 1.5-2.5 hours to transform it into a phase mainly composed of anhydrous gypsum type III. Then cool it to room temperature and lightly grind it to a specific surface area of ​​400-500 m². 2 / kg, to obtain activated gypsum powder;

[0031] S2. Construction of composite expansive aggregate:

[0032] Micron-sized carbide slag, composite active powder, and activated gypsum powder are put into a three-dimensional motion mixer and mixed at 20-40℃ for 30-45 minutes to obtain composite expanded aggregate.

[0033] S3, sustained-release coating:

[0034] The composite expanded aggregate obtained from S2 is preheated to 55-65℃ and put into a high-speed vortex coating machine. Under continuous stirring, the organic slow-release coating agent is sprayed evenly in the form of atomization. The spraying time is controlled at 8-15 minutes so that the organic slow-release coating agent melts on the surface of the composite expanded aggregate particles to form a continuous film. After coating, it is cooled to room temperature to obtain coated composite expanded aggregate.

[0035] S4. Final product preparation:

[0036] The coated composite expansive aggregate obtained from S3 and the interface activator are put into a double helix conical mixer and mixed at 25-30℃ for 20-30 minutes. After uniform mixing, the oil well cement expansive agent is obtained.

[0037] Further, in step S1.2, the grinding aid is a liquid composed of triethanolamine and ethylene glycol in a mass ratio of 1:2;

[0038] The vertical stirred mill has a media filling rate of 60-75%, and the grinding media consists of zirconia balls with a diameter of 3-8 mm.

[0039] Furthermore, in step S3, the high-speed vortex coating machine rotates at 300-600 rpm, and the hot air temperature is controlled at 70-80℃ during the coating process to ensure that the coating agent melts but does not flow; the amount of the organic slow-release coating agent accounts for 1.5-4.0% of the mass of the composite expanded aggregate.

[0040] Thirdly, the technical solution adopted by the present invention is: an application of an oil well cement expansion agent in oil well cement, with oil well cement as the main material, and the dosage of the expansion agent being 3.0-6.0% of the mass of the oil well cement.

[0041] In this invention, the composite expanded aggregate is composed of four industrial solid wastes in a specific ratio: calcium carbide slag, steel slag powder, desulfurized gypsum, and metakaolin. The calcium carbide slag (particle size 5-80 μm) mainly consists of Ca(OH)2, containing small amounts of CaO, CaCO3, etc. The Ca(OH)2 in the calcium carbide slag can rapidly dissolve and release Ca. 2+ and OH - This increases the pH value of the cement slurry pore liquid, creating a strongly alkaline environment for the subsequent dissolution and hydration of active components such as steel slag and metakaolin, thus playing an alkaline activation role. At the same time, the small amount of incompletely dissolved free CaO contained in the carbide slag is key to early expansion. When free CaO hydrates to form Ca(OH)2, its solid phase volume expands by about 97%, which can generate significant expansion stress. Its hydration reaction is rapid and is the main force to compensate for early chemical shrinkage and plastic shrinkage.

[0042] Steel slag powder contains dicalcium silicate, tricalcium silicate, calcium aluminoferrite, RO phase (MgO, FeO, etc. solid solutions), and small amounts of free calcium oxide and free magnesium oxide. The dicalcium silicate and tricalcium silicate contained therein possess potential hydraulic properties and can undergo hydration reactions under strongly alkaline conditions to generate CSH gel, contributing to the strength development of cement stone and acting as a "cementing expansion source." Free magnesium oxide, also known as periclase, hydrates to form Mg(OH)₂ (brucite), and the reaction rate of periclase to form Mg(OH)₂ (brucite) is higher than that of free calcium oxide. O is much slower, with its solid phase volume expanding by about 118%. This expansion occurs in the middle and late stages after the cement paste has hardened, effectively compensating for the autogenous shrinkage and temperature drop shrinkage during the hardening period of the cement stone, and preventing the generation of microcracks in the later stages. Steel slag powder and metakaolin are co-milled, and the co-milling process allows the two to come into full contact and activate each other. The alkaline environment of the steel slag powder promotes the dissolution of the silica-alumina phase in the metakaolin. Meanwhile, the fine metakaolin powder can act as a "micro-grinding medium" in the co-milling process, further refining the steel slag particles, exposing new surfaces, and improving their activity.

[0043] After calcination at 150-180℃, activated desulfurized gypsum mainly transforms into anhydrous gypsum type III (CaSO4•εH2O, ε≈0.5), which has higher solubility. Anhydrous gypsum type III can rapidly dissolve and provide SO4. 2- With the aluminum phase (C3A) in cement or active aluminum sources (such as Al provided by metakaolin) 3+ ) and Ca in the liquid phase 2+ (Mainly provided by carbide slag and cement) The reaction produces needle-like or columnar ettringite (AFt) crystals. The formation of ettringite is accompanied by volume expansion, which is the core driving force of mid-term expansion. By controlling the particle size and crystal form of activated desulfurized gypsum (high-activity anhydrous gypsum type III), the dissolution and reaction rate of activated desulfurized gypsum can be precisely controlled, so that the expansion peak of ettringite appears in the window period after the initial setting and before the final setting of cement paste. At this time, the paste has lost its fluidity but has not yet formed a high-strength structure. The expansion energy can be most effectively converted into the pre-compression stress of the dense structure, rather than causing damage.

[0044] Calcinated metakaolinite, primarily composed of amorphous aluminum silicate oxide (Al₂O₂·2SiO₂), exhibits extremely high pozzolanic activity. The dissolved Al₂O₃... 3+ It is an essential raw material for the formation of ettringite (AFt), and together with the SO4 provided by desulfurization gypsum. 2- Ca provided by calcium carbide slag 2+ Together they form a ternary expansion system of "CaO-Al2O3-CaSO4"; under a strongly alkaline environment, metakaolin undergoes a volcanic ash reaction to generate additional CSH gel and CASH gel. These gels not only enhance the later strength but also refine the pores, improving the density and impermeability of the cement stone.

[0045] In this invention, the interface activator is composed of sodium sulfate, sodium silicate, and triethanolamine in a mass ratio of 5:4:1; sodium sulfate provides additional Na. + and SO4 2- Na + It can accelerate the dissolution of silicate minerals in cement and promote early hydration; SO4 2- It can supplement the sulfur source and combine with prematurely dissolved aluminum ions in the liquid phase to generate a small amount of early AFt, which helps to accelerate the formation of slurry structure. Sodium silicate, as a powerful alkali activator and dispersant, provides silicate ions and strong alkalinity, which can strongly activate the pozzolanic activity of steel slag and metakaolin, prompting them to participate in the reaction earlier and more extensively. At the same time, sodium silicate can form a double electric layer on the surface of solid particles, playing an auxiliary dispersing role and preventing particle agglomeration. Triethanolamine is an important complexing activator and retarding regulator. At low dosage, it can selectively complex C3A and iron phase, delay the early hydration of aluminate minerals, avoid the rapid consumption of gypsum, and create conditions for the continuous formation of ettringite. At the same time, triethanolamine can promote the hydration of C3S, which is beneficial to the early strength development. The combination of sodium sulfate, sodium silicate and triethanolamine forms a regulation of coagulation promotion (C3S hydration), retarding (C3A hydration) and activation (solid waste activity), ensuring that each expansion reaction occurs in the correct time sequence.

[0046] In this invention, the organic slow-release coating agent is a composite wax powder prepared by spray cooling after melting and mixing stearic acid and low molecular weight polyethylene wax at a mass ratio of 1:0.3-0.6. The organic slow-release coating agent forms a continuous, hydrophobic, low-melting-point wax film on the surface of the composite expanded aggregate particles. In the initial stage of cement slurry mixing, this film prevents water molecules from directly and rapidly contacting the internal active components (especially free CaO in carbide slag). As cement hydration releases heat and the slurry temperature rises, when the temperature reaches the melting point range of the composite wax powder (60-75℃), the wax film begins to soften and melt, changing from a continuous and dense state to a porous or fractured state. This process delays the onset time of the core expansion component's contact reaction with water, ensuring that the expansion reaction is effectively suppressed during the mixing and pumping stage when the cement slurry is still in a plastic state, avoiding ineffective early expansion. The expansion reaction is only triggered when the slurry reaches the predetermined position at the bottom of the well, the temperature rises, and the slurry begins to solidify, allowing the expansion energy to be utilized efficiently.

[0047] When the oil well cement expansion agent prepared in this invention is applied to oil well cement, 1. during the mixing and pumping period, the organic wax film effectively coats the aggregate, inhibiting the hydration of internal components. The components in the interface activator begin to dissolve, sodium sulfate and sodium silicate initially increase the alkalinity of the liquid phase, and triethanolamine inhibits the C3A reaction, maintaining good fluidity and pumpability of the system; 2. during the initial to final setting period, the cement hydration releases heat, and the bottom hole temperature, combined with the heat release, raises the slurry temperature to the melting point of the wax film, removing the slow-release barrier. Free CaO in the carbide slag hydrates rapidly first, providing early expansion and compensating for plastic shrinkage, while simultaneously releasing a large amount of Ca. 2+ and OH - The process involves creating a highly alkaline environment, which activates the steel slag and metakaolin, rapidly dissolving the activated desulfurized gypsum. This gypsum combines with the aluminum phase in the cement, the aluminum source provided by the metakaolin, and calcium ions in the liquid phase to generate a large amount of ettringite (AFt), resulting in strong mid-term expansion. At this point, the cement paste has begun to form a structure, and the expansion force can be effectively converted into pre-compression stress, compacting the paste. 3. In the mid-to-late stage of hardening, the ettringite formation reaction continues, and the active C2S in the steel slag continues to hydrate. Free MgO (pericarpegite) begins to hydrate slowly, providing delayed late-stage micro-expansion to compensate for the self-shrinkage and temperature drop shrinkage after cement stone hardening, further improving density. The pozzolanic reaction of the metakaolin continues to generate C-(A)-SH gel, which interweaves with the cement hydration products, refines the pores, strengthens the structure, locks the pre-compression stress generated by the early expansion in a dense microstructure, and improves long-term durability. The sodium silicate and other interfacial activators continue to act, ensuring that the solid waste activity is fully activated.

[0048] Compared with the prior art, the advantages of the present invention are:

[0049] 1. The oil well cement expansion agent prepared by this invention eliminates the volume shrinkage of the cement sheath from the plastic stage to the late hardening stage. In the early stage, the organic coating delays the reaction of free CaO in the carbide slag, causing its expansion to occur before and after the initial setting of the slurry, effectively compensating for chemical shrinkage and plastic shrinkage, and preventing the formation of initial micro-annular gaps. In the middle stage, the large-scale and continuous generation of ettringite (AFt) provides strong expansion force during the critical period of cement stone structure formation. This expansion not only compensates for the shrinkage at this stage, but also generates uniform pre-stress on the initially formed structure, making it more compact. In the later stage, the slow hydration of free MgO in the steel slag provides continuous and mild micro-expansion in the long-term, offsetting the self-shrinkage and temperature drop shrinkage of the cement stone, preventing the initiation and development of micro-cracks in the later stage, fundamentally reducing the width and number of micro-annular gaps between the cement sheath and the casing (first interface) and between the cement sheath and the formation (second interface), and significantly improving the interlayer sealing capacity of the cement sheath.

[0050] 2. This invention utilizes various industrial solid wastes as main raw materials, including carbide slag, steel slag powder, desulfurized gypsum, and metakaolin. These raw materials are widely available and inexpensive, achieving resource utilization of industrial waste, reducing dependence on natural resources, and minimizing environmental pollution caused by solid waste stockpiling. Through scientific and reasonable proportioning and a unique preparation process, these solid wastes exert a synergistic effect in the oil well cement expansion agent, not only solving problems such as large fluctuations in solid waste composition, low activity, or the presence of unfavorable components, but also significantly improving the performance of the expansion agent. Under high-temperature environments, the oil well cement expansion agent of this invention can effectively... Overcoming the problem of diminishing expansion efficiency in traditional expansion agents, this invention exhibits stable and durable expansion performance, providing reliable and effective compensation for oil well cement and ensuring the performance stability of oil well cement under different operating conditions. Furthermore, the application of the oil well cement expansion agent prepared in this invention in oil well cement can regulate the time sequence of each expansion reaction, allowing the early, middle, and late expansion effects to cooperate with each other, efficiently utilizing expansion energy, effectively compensating for the shrinkage of cement stone at different stages, preventing the generation of microcracks, improving the density and impermeability of cement stone, and thus enhancing the long-term durability of oil well cement, providing a strong guarantee for the quality and safety of oil well engineering. Detailed Implementation

[0051] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1

[0053] A method for preparing an oil well cement expansion agent includes the following steps:

[0054] S1. Raw material pretreatment and activation:

[0055] S1.1 Dry the carbide slag in an oven at 110℃ until the moisture content is <1%, and then use an air classifier to separate the 5-80μm micron-sized carbide slag for later use.

[0056] S1.2. Add 30 parts of steel slag powder and 15 parts of metakaolin to a vertical stirred mill and mix thoroughly to obtain a mixture. Then add 0.8% of the mixture weight of grinding aid (triethanolamine and ethylene glycol in a mass ratio of 1:2). Set the media filling rate to 70% and use Φ5mm zirconia balls as grinding media. Grind together for 60 minutes to achieve a specific surface area of ​​650m². 2 / kg, to obtain composite active powder;

[0057] S1.3. 20 parts of desulfurized gypsum were calcined at 165℃ for 2 hours to transform it into a phase mainly composed of anhydrous gypsum type III. Then, it was cooled to room temperature and slightly ground to a specific surface area of ​​450 m². 2 / kg, to obtain activated gypsum powder;

[0058] S2. Construction of composite expansive aggregate:

[0059] 35 parts of micron-sized carbide slag, the composite active powder obtained in S1.2, and the activated gypsum powder obtained in S1.3 were put into a three-dimensional motion mixer and mixed at 30°C for 40 minutes to obtain composite expanded aggregate.

[0060] S3, sustained-release coating:

[0061] The composite expanded aggregate obtained from S2 was preheated to 60°C and put into a high-speed vortex coating machine at 450 rpm. Hot air at 75°C was introduced and 2.5 parts of organic slow-release coating agent (stearic acid: polyethylene wax = 1: 0.45) were sprayed evenly in the form of atomization under continuous stirring. The spraying time was controlled at 10 minutes, so that the organic slow-release coating agent melted on the surface of the composite expanded aggregate particles to form a continuous film. After coating, it was cooled to room temperature to obtain coated composite expanded aggregate.

[0062] S4. Final product preparation:

[0063] The coated composite expansive aggregate obtained from S3 was added to a double-spiral conical mixer with 5 parts of interface activator (sodium sulfate: sodium silicate: triethanolamine = 5:4:1) and mixed at 28°C for 25 minutes. After uniform mixing, the oil well cement expansive agent was obtained.

[0064] Cement grout preparation:

[0065] The standard cement slurry formula is: 600 parts of Grade G oil well cement and 264 parts of fresh water (water-cement ratio 0.44).

[0066] Expanding agent cement slurry formulation: In the above-mentioned benchmark cement slurry formulation, 4.0% of the mass of G-grade oil well cement and 24.0 parts of the expanding agent of this embodiment are added externally.

[0067] Example 2

[0068] A method for preparing an oil well cement expansion agent includes the following steps:

[0069] S1. Raw material pretreatment and activation:

[0070] S1.1 Dry the carbide slag in an oven at 110℃ until the moisture content is <1%, and then use an air classifier to separate the 5-80μm micron-sized carbide slag for later use.

[0071] S1.2. Add 28 parts of steel slag powder and 14 parts of metakaolin to a vertical stirred mill and mix thoroughly to obtain a mixture. Then add 0.8% of the mixture weight of grinding aid (triethanolamine and ethylene glycol in a mass ratio of 1:2). Set the media filling rate to 70% and use Φ5mm zirconia balls as grinding media. Grind together for 60 minutes to achieve a specific surface area of ​​650m². 2 / kg, to obtain composite active powder;

[0072] S1.3. 18 parts of desulfurized gypsum were calcined at 165℃ for 2 hours to transform it into a phase mainly composed of anhydrous gypsum type III. Then, it was cooled to room temperature and slightly ground to a specific surface area of ​​450 m². 2 / kg, to obtain activated gypsum powder;

[0073] S2. Construction of composite expansive aggregate:

[0074] Forty parts of micron-sized carbide slag, the composite active powder obtained in S1.2, and the activated gypsum powder obtained in S1.3 were put into a three-dimensional motion mixer and mixed at 30°C for 40 minutes to obtain composite expanded aggregate.

[0075] S3, sustained-release coating:

[0076] The composite expanded aggregate obtained from S2 was preheated to 60°C and put into a high-speed vortex coating machine at 450 rpm. Hot air at 75°C was introduced and 2.5 parts of organic slow-release coating agent (stearic acid: polyethylene wax = 1: 0.45) were sprayed evenly in the form of atomization under continuous stirring. The spraying time was controlled at 10 minutes, so that the organic slow-release coating agent melted on the surface of the composite expanded aggregate particles to form a continuous film. After coating, it was cooled to room temperature to obtain coated composite expanded aggregate.

[0077] S4. Final product preparation:

[0078] The coated composite expansive aggregate obtained from S3 was added to a double-spiral conical mixer with 5 parts of interface activator (sodium sulfate: sodium silicate: triethanolamine = 5:4:1) and mixed at 28°C for 25 minutes. After uniform mixing, the oil well cement expansive agent was obtained.

[0079] Cement grout preparation:

[0080] The standard cement slurry formula is: 600 parts of Grade G oil well cement and 264 parts of fresh water (water-cement ratio 0.44).

[0081] Expanding agent cement slurry formulation: In the above-mentioned benchmark cement slurry formulation, 4.0% of the mass of G-grade oil well cement and 24.0 parts of the expanding agent of this embodiment are added externally.

[0082] Example 3

[0083] A method for preparing an oil well cement expansion agent includes the following steps:

[0084] S1. Raw material pretreatment and activation:

[0085] S1.1 Dry the carbide slag in an oven at 110℃ until the moisture content is <1%, and then use an air classifier to separate the 5-80μm micron-sized carbide slag for later use.

[0086] S1.2. Add 32 parts of steel slag powder and 16 parts of metakaolin to a vertical stirred mill and mix thoroughly to obtain a mixture. Then add 0.8% of the mixture weight of grinding aid (triethanolamine and ethylene glycol in a mass ratio of 1:2). Set the media filling rate to 70% and use Φ5mm zirconia balls as grinding media. Grind together for 60 minutes to achieve a specific surface area of ​​650m². 2 / kg, to obtain composite active powder;

[0087] S1.3. 22 parts of desulfurized gypsum were calcined at 165℃ for 2 hours to transform it into a phase mainly composed of anhydrous gypsum type III. Then, it was cooled to room temperature and slightly ground to a specific surface area of ​​450 m². 2 / kg, to obtain activated gypsum powder;

[0088] S2. Construction of composite expansive aggregate:

[0089] Thirty parts of micron-sized carbide slag, the composite active powder obtained in S1.2, and the activated gypsum powder obtained in S1.3 were put into a three-dimensional motion mixer and mixed at 30°C for 40 minutes to obtain composite expanded aggregate.

[0090] S3, sustained-release coating:

[0091] The composite expanded aggregate obtained from S2 was preheated to 60°C and put into a high-speed vortex coating machine at 450 rpm. Hot air at 75°C was introduced and 2.5 parts of organic slow-release coating agent (stearic acid: polyethylene wax = 1: 0.45) were sprayed evenly in the form of atomization under continuous stirring. The spraying time was controlled at 10 minutes, so that the organic slow-release coating agent melted on the surface of the composite expanded aggregate particles to form a continuous film. After coating, it was cooled to room temperature to obtain coated composite expanded aggregate.

[0092] S4. Final product preparation:

[0093] The coated composite expansive aggregate obtained from S3 was added to a double-spiral conical mixer with 5 parts of interface activator (sodium sulfate: sodium silicate: triethanolamine = 5:4:1) and mixed at 28°C for 25 minutes. After uniform mixing, the oil well cement expansive agent was obtained.

[0094] Cement grout preparation:

[0095] The standard cement slurry formula is: 600 parts of Grade G oil well cement and 264 parts of fresh water (water-cement ratio 0.44).

[0096] Expanding agent cement slurry formulation: In the above-mentioned benchmark cement slurry formulation, 4.0% of the mass of G-grade oil well cement and 24.0 parts of the expanding agent of this embodiment are added externally.

[0097] Example 4

[0098] A method for preparing an oil well cement expansion agent includes the following steps:

[0099] S1. Raw material pretreatment and activation:

[0100] S1.1 Dry the carbide slag in an oven at 110℃ until the moisture content is <1%, and then use an air classifier to separate the 5-80μm micron-sized carbide slag for later use.

[0101] S1.2. Add 30 parts of steel slag powder and 15 parts of metakaolin to a vertical stirred mill and mix thoroughly to obtain a mixture. Then add 0.8% of the mixture weight of grinding aid (triethanolamine and ethylene glycol in a mass ratio of 1:2). Set the media filling rate to 70% and use Φ5mm zirconia balls as grinding media. Grind together for 60 minutes to achieve a specific surface area of ​​650m². 2 / kg, to obtain composite active powder;

[0102] S1.3. 20 parts of desulfurized gypsum were calcined at 165℃ for 2 hours to transform it into a phase mainly composed of anhydrous gypsum type III. Then, it was cooled to room temperature and slightly ground to a specific surface area of ​​450 m². 2 / kg, to obtain activated gypsum powder;

[0103] S2. Construction of composite expansive aggregate:

[0104] 35 parts of micron-sized carbide slag, the composite active powder obtained in S1.2, and the activated gypsum powder obtained in S1.3 were put into a three-dimensional motion mixer and mixed at 30°C for 40 minutes to obtain composite expanded aggregate.

[0105] S3, sustained-release coating:

[0106] The composite expanded aggregate obtained from S2 was preheated to 60°C and put into a high-speed vortex coating machine at 450 rpm. Hot air at 75°C was introduced and 3.5 parts of organic slow-release coating agent (stearic acid: polyethylene wax = 1: 0.45) were sprayed evenly in the form of atomization under continuous stirring. The spraying time was controlled at 10 minutes, so that the organic slow-release coating agent melted on the surface of the composite expanded aggregate particles to form a continuous film. After coating, it was cooled to room temperature to obtain coated composite expanded aggregate.

[0107] S4. Final product preparation:

[0108] The coated composite expansive aggregate obtained from S3 was added to a double-spiral conical mixer with 7 parts of interfacial activator (sodium sulfate: sodium silicate: triethanolamine = 5:4:1) and mixed at 28°C for 25 minutes. After uniform mixing, the oil well cement expansive agent was obtained.

[0109] Cement grout preparation:

[0110] The standard cement slurry formula is: 600 parts of Grade G oil well cement and 264 parts of fresh water (water-cement ratio 0.44).

[0111] Expanding agent cement slurry formulation: In the above-mentioned benchmark cement slurry formulation, 4.0% of the mass of G-grade oil well cement and 24.0 parts of the expanding agent of this embodiment are added externally.

[0112] Comparative Example 1

[0113] The difference from Example 1 is that the co-grinding process in step S1.2 is omitted; the steel slag powder is ground separately to a specific surface area of ​​about 400 m² / kg; the metakaolin is used directly as raw powder (specific surface area of ​​about 15000 m² / kg); the two are not co-grinded and are directly mixed with other aggregate components in step S2; the rest of the formula and process are exactly the same as in Example 1.

[0114] Comparative Example 2

[0115] The difference from Example 1 is that the coating process in step S3 is omitted; the uncoated composite expanded aggregate obtained in step S2 is directly mixed with the interface activator in step S4; the rest of the formulation and process are exactly the same as in Example 1.

[0116] Comparative Example 3

[0117] The commercially available mainstream calcium sulfoaluminate oil well cement expansion agent was used; the dosage was also 4.0% of the mass of G-grade oil well cement. The cement slurry preparation was the same as the cement slurry formula in Example 1, except that the expansion agent was replaced with a commercially available product.

[0118] Comparative Example 4

[0119] Only the dried and graded micron-sized carbide slag from Example 1 was used; the dosage was 4.0% of the mass of G-grade oil well cement (i.e., 24.0 parts of pure carbide slag). The cement slurry was prepared in the same way as the cement slurry formula in Example 1, except that the expanding agent was replaced with carbide slag.

[0120] Comparative Example 5

[0121] The blank control group consisted of a standard cement slurry without any expansion agent: 600 parts of G-grade oil well cement and 264 parts of fresh water (water-cement ratio 0.44).

[0122] Experimental Example

[0123] I. Experimental methods and basis:

[0124] All cement slurry performance tests were conducted in accordance with the petroleum industry standard SY / T 5504.1-2013 "Evaluation Method for Oil Well Cement Admixtures" and the American Petroleum Institute (API) SPEC 10A "Specifications for Oil Well Cement Materials and Tests".

[0125] 1. Conventional performance testing of cement grout;

[0126] Thickening time: The time required for the slurry to reach a consistency of 100 Bc from the start of stirring was tested using a Chandler 7660 pressurized thickener at 65°C and 40 MPa.

[0127] Rheology: The six-speed readings of the cement paste were measured at 25°C using an OFI 800 rotational viscometer to calculate the plastic viscosity (PV) and dynamic shear force (YP).

[0128] Free liquid: Pour the prepared cement slurry into a 250mL graduated cylinder, let it stand in a 65℃ water bath for 2 hours, and then measure the volume of the clear liquid precipitated at the top.

[0129] 2. Cement stone expansion performance test;

[0130] Test method: Non-contact laser displacement sensor method was used. Cement slurry was injected into a polytetrafluoroethylene mold with an inner diameter of 50 mm and a height of 100 mm, and then placed in a constant temperature and pressure curing autoclave at 65℃ and 20 MPa for curing.

[0131] Test basis: Referring to the principle of ASTM C806 "Standard Test Method for Expansion of Hardened Cement Paste", a high-precision laser sensor was used to continuously measure the radial displacement of the specimen.

[0132] Data processing: The radial expansion rate (%) was recorded for 24 hours, 7 days, and 28 days respectively. The calculation formula is: (D t -D0) / D0×100%, where D0 is the initial inner diameter, D t The inner diameter after curing for t time.

[0133] 3. Testing of the mechanical and bonding properties of cement stone;

[0134] Compressive strength: 2-inch (50.8 mm) cubic specimens were prepared using cement grout, cured at 65°C and normal pressure to the specified age, and tested according to API specifications using an AG-I 250kN universal testing machine.

[0135] Interface bond strength: A simulated casing bond strength tester was used. Cement grout was injected into the annular space between the treated inner wall of the steel ring (simulated casing) and the outer core (or simulated formation). After curing at 65℃ and 20MPa for 7 days, the maximum shear stress (MPa) required to peel the cement ring off the steel ring was tested.

[0136] 4. Resistance to gas channeling test;

[0137] Test method: Static anti-gas leakage simulator (SPN tester).

[0138] Test basis: The pressure loss factor (SPN value) is calculated by measuring the hydrostatic pressure transmission capacity of cement slurry during the setting transition period (consistency 30Bc to 100Bc).

[0139] Evaluation criteria: The lower the SPN value, the stronger the cement grout's ability to maintain hydrostatic pressure and resist gas intrusion. Generally, SPN < 1.5 is considered to have excellent gas intrusion prevention capabilities.

[0140] II. Experimental Data and Analysis:

[0141] Table 1. Test results of conventional properties of cement grout (Test conditions: 65℃ / 40MPa)

[0142] Group Thickening time (min) Initial consistency (Bc) Free liquid (mL) Plastic viscosity PV (cP) Dynamic shear force YP (Pa) SPN value Example 1 158 19 1.2 45 6.8 1.3 Example 2 152 21 1.5 48 7.2 1.4 Example 3 161 18 1.0 43 6.5 1.2 Example 4 168 16 0.8 40 6.0 1.1 Comparative Example 1 142 26 2.8 55 9.5 1.9 Comparative Example 2 95 32 4.5 62 12.0 3.6 Comparative Example 3 175 23 2.0 50 8.0 1.9 Comparative Example 4 82 38 6.0 70 15.0 4.3 Comparative Example 5 185 12 0.5 35 5.5 2.7

[0143] As can be seen from the table above, Examples 1-4 have moderate thickening times (152-168 min), ensuring a safe pumping window; Comparative Examples 2 and 4, due to lack of coating or single components, have excessively rapid early hydration and excessively short thickening times (<100 min), posing engineering risks; Examples 1-4 have low initial consistency (16-21 Bc), less free liquid (<1.5 mL), and moderate PV and YP values, indicating good slurry fluidity and excellent settling stability. All comparative examples are inferior to the examples in these indicators; The SPN values ​​of Examples 1-4 are only 1.1-1.4, far superior to Comparative Examples 3 (1.9) and 5 (2.7), and significantly superior to Comparative Examples 2 (3.6) and 4 (4.3). This proves that the coating slow-release and multi-component synergistic mechanism of the present invention effectively maintains the pressure of cement slurry during the dangerous transition period and has outstanding anti-gas channeling ability.

[0144] Table 2. Test results of cement stone expansion performance (curing conditions: 65℃ / 20MPa)

[0145] Group 24h expansion rate (%) 7-day expansion rate (%) 28-day expansion rate (%) Notes (28d appearance) Example 1 0.16 1.28 1.38 Complete, without cracks Example 2 0.19 1.35 1.45 Complete, without cracks Example 3 0.14 1.22 1.32 Complete, without cracks Example 4 0.11 1.18 1.30 Complete, without cracks Comparative Example 1 0.09 0.88 0.95 Complete, without cracks Comparative Example 2 0.38 1.55 0.75* The surface has fine lines Comparative Example 3 0.06 0.98 0.65* whole Comparative Example 4 0.42 0.48 0.35 There is a shrinkage pit on the top. Comparative Example 5 -0.15 -0.38 -0.52 Overall shrinkage, edge separation

[0146] Note: Values ​​marked with "*" indicate that shrinkage occurred later (28-day expansion rate < 7-day expansion rate).

[0147] As shown in the table above, Examples 1-4 exhibit an ideal curve of "moderate early expansion, major expansion in the middle stage, and stable expansion in the later stage." The 24-hour expansion rate (0.11-0.19%) compensated for plastic shrinkage; the 7-day expansion rate (1.18-1.35%) was key to compensating for hardening shrinkage; the 28-day expansion rate was stable or slightly increased, demonstrating the dual role of free MgO expansion and structural stability in the later stage. The expansion rates of Comparative Example 1 (unco-milled) at each stage were significantly lower than those of Examples 1, proving that co-milling activation of steel slag and metakaolin is crucial for fully activating activity and achieving synergistic expansion; Comparative Example 2 (uncoated) showed early expansion... Excessive expansion (0.38%) occurred in the early stage, but severe shrinkage (0.75%) occurred in the later stage. This was because the early reaction consumed too much raw material, resulting in insufficient expansion source in the middle and later stages. This proves the necessity of organic slow-release coating for controlling reaction sequence and achieving full-process compensation. Comparative Example 3 (traditional expansion agent) showed insufficient expansion in the early and middle stages, and more obvious shrinkage in the later stage, indicating that its effectiveness had begun to decline at 65℃ and its long-term volume stability was not as good as that of this invention. Comparative Example 4 (pure carbide slag) only showed early expansion and almost no compensation ability in the middle and later stages. Moreover, the sample showed shrinkage defects, proving that a single expansion source cannot meet the engineering requirements.

[0148] Table 3. Test results of mechanical and bonding properties of cement stone (curing conditions: 65℃ / 20MPa)

[0149] Group 24-hour compressive strength (MPa) 28-day compressive strength (MPa) 7-day interfacial bond strength (MPa) Example 1 18.8 45.5 3.9 Example 2 19.5 46.8 4.1 Example 3 18.2 44.9 3.7 Example 4 17.5 43.6 3.6 Comparative Example 1 16.0 39.2 2.7 Comparative Example 2 14.8 37.5 2.3 Comparative Example 3 17.0 41.0 2.9 Comparative Example 4 13.2 33.8 1.9 Comparative Example 5 20.5 48.2 2.4

[0150] As can be seen from the table above, the 24h and 28d compressive strengths of Examples 1-4 are comparable to those of the blank control group (Comparative Example 5), and in some cases even higher (such as Example 2). This indicates that the expansion of the present invention does not come at the expense of strength, but is enhanced by pre-compression. The strengths of all comparative examples are lower or significantly lower than those of the Examples. The interfacial bonding strength (3.6-4.1 MPa) of Examples 1-4 far exceeds that of all comparative examples, and is 50%-70% higher than that of the blank control group (2.4 MPa). This proves that the expansion agent prepared in this application improves the interlayer sealing ability, and the continuous, outward micro-expansion force greatly improves the bonding quality between the cement ring and the sleeve.

[0151] In summary, the oil well cement expanding agent of the present invention exhibits significant advantages in terms of conventional cement slurry performance, cement stone expansion performance, and mechanical and cementing properties. Examples 1-4 show moderate thickening time, low initial consistency, low free liquid, and moderate PV and YP values, indicating good slurry fluidity and excellent settling stability. Simultaneously, the low SPN value demonstrates outstanding gas channeling prevention capability. Regarding cement stone expansion performance, Examples 1-4 exhibit an ideal curve of "moderate early expansion, major expansion in the middle stage, and stable expansion in the later stage," effectively compensating for the shrinkage of the cement stone at different stages. Furthermore, Examples 1-4 demonstrate excellent compressive strength and interfacial cementing strength, without sacrificing strength due to expansion; in fact, strength is enhanced, and the interfacial cementing strength far exceeds that of all comparative examples, significantly improving interlayer sealing capability. In contrast, the comparative examples show significant deficiencies in all performance aspects, further demonstrating the superiority and practicality of the oil well cement expanding agent of the present invention.

[0152] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An oil well cement expanding agent, characterized in that, It is prepared from the following raw materials in parts by weight: Composite expanded aggregate: 90-100 parts; Interface activator: 3-8 parts; Organic sustained-release coating agent: 1.5-4 parts; The composite expanded aggregate is prepared from the following raw materials in parts by weight: Carbide slag: 30-45 parts; Steel slag powder: 25-35 parts; Desulfurized gypsum: 15-25 parts; Metakaolin: 10-20 parts.

2. The oil well cement expanding agent according to claim 1, characterized in that, The particle size of the carbide slag and steel slag powder is 5-80μm, and the carbide slag and steel slag powder account for 60-70% of the total mass of the composite expanded aggregate.

3. The oil well cement expanding agent according to claim 1, characterized in that, The particle size of the desulfurized gypsum and metakaolin is 0.5-5μm, and the desulfurized gypsum and metakaolin account for 30-40% of the total mass of the composite expansive aggregate.

4. The oil well cement expanding agent according to claim 1, characterized in that, The interface activator is composed of sodium sulfate, sodium silicate, and triethanolamine; The mass ratio of sodium sulfate, sodium silicate and triethanolamine is 5:4:1, and its fineness is ≤10μm.

5. The oil well cement expanding agent according to claim 4, characterized in that, The organic slow-release coating agent is a composite wax powder prepared by melting and mixing stearic acid and low molecular weight polyethylene wax at a mass ratio of 1:0.3-0.6 and then spray cooling. The organic slow-release coating agent has a melting point range of 60-75℃ and a particle size of 10-30μm.

6. The oil well cement expanding agent according to claim 5, characterized in that, The molecular weight of the low molecular weight polyethylene wax is 2000-3000.

7. A method for preparing an oil well cement expanding agent according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Raw material pretreatment and activation: S1.1 Dry the carbide slag at 105-120℃ until the moisture content is <1%, and then use an air classifier to separate the 5-80μm micron-sized carbide slag for later use. S1.2, the steel slag micro-powder and the metakaolin are put into a vertical stirring mill, stirred uniformly to obtain a mixture, then 0.5-1.0% of grinding aids by weight of the mixture is added, and the mixture is ground together for 45-90 minutes, so that the specific surface area of the mixture reaches 550-750 m 2 / kg, to obtain a composite active powder; S1.3 Calcine the desulfurized gypsum at 150-180℃ for 1.5-2.5 hours to transform it into a phase mainly composed of anhydrous gypsum type III. Then cool it to room temperature and lightly grind it to a specific surface area of ​​400-500 m². 2 / kg, to obtain activated gypsum powder; S2. Construction of composite expansive aggregate: Micron-sized carbide slag, composite active powder, and activated gypsum powder are put into a three-dimensional motion mixer and mixed at 20-40℃ for 30-45 minutes to obtain composite expanded aggregate. S3, sustained-release coating: The composite expanded aggregate obtained from S2 is preheated to 55-65℃ and put into a high-speed vortex coating machine. Under continuous stirring, the organic slow-release coating agent is sprayed evenly in the form of atomization. The spraying time is controlled at 8-15 minutes so that the organic slow-release coating agent melts on the surface of the composite expanded aggregate particles to form a continuous film. After coating, it is cooled to room temperature to obtain coated composite expanded aggregate. S4. Final product preparation: The coated composite expansive aggregate obtained from S3 and the interface activator are put into a double helical conical mixer and mixed at 25-30℃ for 20-30 minutes. After uniform mixing, the oil well cement expansive agent is obtained.

8. The method for preparing an oil well cement expanding agent according to claim 7, characterized in that, In step S1.2, the grinding aid is a liquid composed of triethanolamine and ethylene glycol in a mass ratio of 1:2; The vertical stirred mill has a media filling rate of 60-75%, and the grinding media consists of zirconia balls with a diameter of 3-8 mm.

9. The method for preparing an oil well cement expanding agent according to claim 7, characterized in that, In step S3, the high-speed vortex coating machine rotates at 300-600 rpm, and the hot air temperature is controlled at 70-80℃ during the coating process to ensure that the coating agent melts but does not flow; the amount of the organic slow-release coating agent accounts for 1.5-4.0% of the mass of the composite expanded aggregate.

10. The application of an oil well cement expanding agent according to any one of claims 1-6 in oil well cement, wherein oil well cement is the main material, characterized in that, The amount of the expansion agent is 3.0-6.0% of the mass of the oil well cement.